THERMAL CLASS AND TEMPERATURE RISE

My doubt is " If we have given the thermal class, it means that it will withstand for that respective temperature rise say example: if Thermal Class of F (155°C) is considered, then the temperature rise is 105°C (considering max ambient temp of 40°C) " Please clarify whether my understanding is correct.

Why both datas are required. Why not simply Thermal class.

Thanks in advance.

RE: THERMAL CLASS AND TEMPERATURE RISE

On large machines it is common to run a Class F insulation system under Class B limits, or more recently a Class H system under Class F limits. By keeping the insulation cooler than strictly necessary the life can be signifcantly extended. The Arrenhius equation predicts that every 10°C reduction in temperature will double the service life, all other factors being equal.

----------------------------------If we learn from our mistakes I'm getting a great education!

RE: THERMAL CLASS AND TEMPERATURE RISE

I heard that limiting temperature rises one step lower than those applicable for the installed insulation thermal class has another reason too - the insulation alongwith the stator conductor is bent to route the same in the core slots, as required during winding the stator in the factory. This process of bending introduces stress in the insulation and thus derating of the insulation as above is important for assured life of the motor.

RE: THERMAL CLASS AND TEMPERATURE RISE

I think i have posted this before, but we run our generating sets with generators at class F rises, with the generator wound with class H insulation (400V generators).

If you compare the generator efficiency, then you save about 1 percentage point in having a larger generator with class F rise, rather than a smaller generator with (hotter) class H rise. "I squared R" copper losses, basically.

For base load - work out the cost of fuel of this 1% over 15 years; for standby, work out the capital cost saving of a smaller class H machine, over the more expensive class F machine

Of course, the Class F rise generator will suffer less temperature stress and will statistically last longer than the class H rise machine.

RE: THERMAL CLASS AND TEMPERATURE RISE

Only for record :I am not sure one does design an electric machine less voluminous based on higher conductor insulation class-above all the manufacturerdeclares rated load is based on the lower class. The force applied to the winding by electromagnetically field depends on product of magnetic fluxdensity [B] and the amperes per m[or per inch] of the stator circumference and that does not depend on insulating class -more amperes per m-less gausses [or Wb/m^2].The stator inner diameter depend on this force-and in turn depends on rated power.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Resources

ENGINEERING.com surveyed 364 product development professionals to glean insights into how their teams are performing today, and what technologies are most useful to support their processes. Download Now

3D printing has quickly expanded beyond the realm of prototyping and into the world of end part manufacturing. Desktop 3D printers need not be used for making parts themselves, but as a secondary process for producing tools. Download Now

Creating tooling for injection molding is an expensive and complex proposition. Until recently, the only way to avoid tooling defects causing air traps, voids, shrinkage and the like was to employ a time-consuming and tedious physical prototyping process. Download Now